THE REACTION-KINETICS, DECOMPOSITION PATHWAYS AND INTERMEDIATE FORMATIONS OF PHENOL IN OZONATION, UV/O3 AND UV/H2O2 PROCESSES

Recently, advanced oxidation processes (AOPs) have been developed as an emerging technology for treating hazardous organics treatment in wastewater and groundwater. In this paper, the phenol decomposition pathways and intermediates in ozonation and two AOPs (e.g. UV/ozone, UV/hydrogen peroxide) were studied in a photochemical pilot reactor utilizing 5000 W low-pressure mercury lamp. It was observed that, in the UV/hydrogen peroxide system, phenol was first oxidized by hydroxyl radical into hydroquinone and catechol which finally decomposed into organic acids and carbon dioxide. Additionally, some other higher molecular weight products such as 4-phenoxy phenol, 2,2-dimethoxyethyl benzene, alpha-methoxy-alpha-methyl benzeneethanol, etc. were also produced. However, in the ozonation process phenol was oxidized into hydroquinone and catechol which were degraded into acids and carbon dioxide without high molecular weight byproducts. In the UV/ozone process, the major reaction pathway was similar to that of ozonation, but some 4-phenoxy phenol was formed and decomposed ultimately.